Interpretive Summary: The fungus Fusarium verticillioides can cause disease on corn and contaminate kernels with toxins which are harmful to humans as well as animals and presents a food safety concern. The research described here is aimed at understanding environmental factors that influence the production of toxins. Water activity is one environmental factor known to affect toxin production and might have a role during the interaction of the fungus with corn in the field. The research reported here shows that water activity has an effect on the expression of genes required for toxin biosynthesis and thus has an effect on toxin accumulation. This research provides insight into the relationship between water activity, gene expression, and toxin production and may be used to engineer strategies to maintain water activity in the corn field to attempt to reduce toxin accumulation.

Technical Abstract:
Fusarium verticillioides is a maize-pathogen that causes ear and stalk rot and produces toxic secondary metabolites including fumonisins and bikaverin. Fumonisins are known to cause disease in animals and humans; bikaverin is a pigment associated with self-defense. Water activity (aw) is one of the many environmental factors known to influence secondary metabolite production in filamentous fungi. The biosynthetic pathways and gene clusters of these metabolites are well described, however, the regulation of gene expression and metabolite production are not fully understood. Here, we investigated the influence of aw on the expression of fumonisin and bikaverin pathway genes, and on toxin production. F. verticillioides strains were cultured at two aw (0.955-0.990); gene expression and secondary metabolite production were assayed at 14 and 21 days post inoculation. Gene expression and toxin production were greatest at high aw. These results show a significant influence of aw on secondary metabolite gene expression and metabolites production.